Fuel composition with improved lubricity performance

ABSTRACT

This invention provides a fuel composition having a sulphur content of not more than 50 ppm by weight and comprising at least 50 ppm based on the total weight of the fuel composition of at least one fused polycyclic aromatic compound which comprises at least one exocyclic group containing nitrogen wherein the nitrogen is attached directly to a ring carbon atom. Specific examples of such compounds include 1-amino naphthalene, 1,8-diaminonaphthalene, or 5-aminoindole, 2-(2-aminophenyl)indole and 8-aminoquinoline. These compounds are capable of improving the antiwear and lubricity properties of a low sulphur fuel when compared with that of the same fuel in the absence of such compounds.

This invention relates to fuel compositions of low sulphur content whichcontain at least one component capable of enhancing the lubricity ofsuch low sulphur fuels.

Fuels such as diesel are widely used in automotive transport due totheir low cost. However, one of the problems with such fuels is thepresence of relatively high concentrations of sulphur containingcompounds. Excessive sulphur contributes to exhaust particulateemissions and can also degrade the effectiveness of some exhaustafter-treatment technology which is being introduced in response toregulated limits on exhaust emissions. As a result, the permitted levelof sulphur in diesel fuel has been progressively reduced over the yearsand further reductions are planned for the future. Whilst reduction insulphur content can be readily achieved by well known processes such aseg hydrodesulphurisation which is generally carried out in the presenceof a catalyst, such process also adversely affects the lubricity of theresultant desulphurised product. Consequently, it is necessary toformulate compositions which are low in sulphur content but are also ofthe desired lubricity in order to minimise wear and friction and thusprotect against damage to the injection system of a diesel engine. Ithas hitherto been the practice to add anti-wear agents to suchformulations including fatty acid esters, lactones, polyoxyalkyleneethers, amino compounds and the like for this purpose. However,compositions containing compounds such as esters are expensive in termsof both material and storage costs. An article by D. Wei et al inLubrication Science, 1989, 2(1), pp 63-67 entitled “The Influence ofChemical Structure of Certain Nitrogen-Containing Organic Compounds onTheir Antiwear Effectiveness: The Critical Role of Hydroxy Group”discloses that some heterocyclic nitrogen compounds have a beneficialeffect on the antiwear performance of base stocks. This author goes onto state that hydroxy groups involved in some nitrogen-containingcompounds have been found to improve their antiwear performancesignificantly and states that hydroxy substituted benzothiazoles aremost effective in wear reduction and anti-scuffing. With this in viewthe author reports the results of the tests carried out on films formedon rubbing surfaces by the benzo-derivatives of pyridine and thiazole,with or without hydroxy groups on the rings. The article concludes thatprotective films formed on rubbing surfaces by the above heterocycliccompounds bearing a hydroxy group are significantly different from thoseproduced by the analogous compounds without a hydroxyl group.

Recently published EP-A-0885947 discloses the use of various additivesto fuel oil compositions which contain no more than 0.05 wt % of sulphurand having a T₉₅ of <350° C., the additives being (a) an ashlessdispersant comprising an acylated nitrogen compound and (b) amonocarboxylic acid having from 2-50 carbon atoms. There is no mentionof fused polycyclic amines or of any fuel containing <50ppm of sulphur.Again, prior published WO 98/16601 claims a fuel oil compositionobtainable by the addition of a minor proportion of a compoundcomprising one or more aromatic ring systems wherein at least one of thering systems bears as substituents (i) one or more hydrocarbon groupsimparting oil solubility to the compound, (ii) one or more hydroxylgroups or derivatives thereof or both, and (iii) one or more amine saltgroups. The sulphur concentration of the fuel oil is said to be ≦0.02 wt%. None of the amine salts described, however, are attached directly toa ring carbon atom and no fused polycyclic aromatic amines aredisclosed.

The use of compounds such as benzothiazoles will add to the sulphurcontent of such fuels and consequently derogate from the objective ofachieving low Sulphur fuels. Moreover, it has also been found that it isnot necessary for the antiwear additive to be a heterocyclic compound.The desired objective can be achieved equally well by using antiwearadditives based on polycyclic compounds containing exocyclic nitrogengroups.

The present invention therefore provides a fuel composition having asulphur content of not more than 50 ppm by weight and comprising atleast 50 ppm based on the total weight of the fuel composition of atleast one fused polycyclic aromatic compound which comprises at leastone exocyclic group containing nitrogen wherein the nitrogen is attacheddirectly to a ring carbon atom.

The sulphur content of the fuel composition is preferably less than 50ppm by weight and more preferably less than 40 ppm by weight. Such lowsulphur levels can be achieved in a number of ways. For instance, thismay be achieved by well known methods such as eg, catalytichydrodesulphurisation. Typically, the present invention is applicable toa broad range of petroleum fuels from light boiling gasoline (boilingrange from 120-140° C.). The most common distillate fuels are kerosene,jet fuels, diesel fuels and heating oils. The lubricity properties ofultra-low sulphur (50 ppm or less) base fuels with a T₉₅ of suitably370° C., preferably 360° C., particularly benefit from the presence ofthe nitrogen compounds referred to above. Especially, the lubricityproperties are more of an issue with diesel fuels because diesel fuelinjection pumps are more sensitive to wear problems. The base fuels maycomprise mixtures of saturated, olefinic and aromatic hydrocarbons andthese can be derived from straight run streams, thermally orcatalytically cracked hydrocarbon feedstocks, hydrocracked petroleumfractions, catalytically reformed hydrocarbons, or syntheticallyproduced hydrocarbon mixtures. The present invention is particularlyapplicable to diesel fuels that have recently been introduced into theUK market and are generally referred to as ultra-low sulphur automotivediesel oils (hereafter “ULSADO” and is sampled eg from Esso's FawleyRefinery).

The fused polycyclic aromatic compound which has at least one exocyclicgroup containing nitrogen wherein the nitrogen is attached directly to aring carbon atom is capable of acting as an antiwear and lubricityenhancing additive for low sulphur fuels according to the invention. Theexpression “fused polycyclic aromatic compound” as used herein andthroughout the specification is meant that said compound comprises anaromatic moiety which has at least two fused rings of which at least oneis an aromatic ring, which aromatic ring may in turn be a heterocyclicring, whether or not the remaining ring(s) in the fused polycyclicstructure are aromatic or carry other hydrocarbyl or functional groupssuch as alkyl, hydroxyl or ketonic or ester groups. One such examplewhere a cycloaliphatic ring is fused with an aromatic/heterocyclic ringis 1-amino indan and another example is an amino anthraquinone.

The exocyclic amino group may also be attached directly to a carbon atomof a ring which is itself attached to but is not part of the fusedpolycyclic ring structure.

Where the fused polycyclic aromatic compound contains a heterocyclicring, the heteroatom may be nitrogen or oxygen.

The exocyclic group containing nitrogen may be a primary or a secondaryamino group and may carry hydrogen and/or hydrocarbyl groups, suchhydrocarbyl groups being aliphatic, cycloaliphatic or aromatic in natureand is preferably a primary amino group. In this context, it is worthnoting that compounds having two exocyclic nitrogen groups arepreferable to compounds which have only one exocyclic nitrogen group.Furthermore, where such compounds have more than one exocyclic nitrogengroup, especially primary amino groups, it is even more preferable thatthese groups are in close proximity and in non-hindered position on thefused polycyclic compound. Thus, it is preferable that the exocyclicnitrogen groups are attached to adjacent carbon atoms, such as eg the1,2-, 2,3-, 3,4-carbon atoms, or, the 1,8-positions of a binuclearstructure of eg the diamino naphthalene type, or, eg the 1,7-positions adiamino indan type. As will be apparent, in the latter two instances,the amino groups are on adjacent carbon atoms if the fused carbonlinking the two rings is ignored. Examples of such compounds containingan exocyclic group containing nitrogen wherein the nitrogen is directlyattached to a ring carbon atom include inter alia 5-aminoindole, 8-aminoquinoline, 1-aminonaphthalene and 1,8-diaminonaphthalene whereas2-(2-aminophenyl) indole is an example of a compound in which theexocyclic amino group is directly attached to a ring carbon atom whereinthe ring itself is attached to a fused polycyclic aromatic compound, ieindole. Where the fused polycyclic aromatic compound contains at leastone secondary amino group, it is preferable that the hydrocarbylsubstituents on this secondary amino group are aliphatic, morepreferably a C1-C4 alkyl group.

In this context it is worth noting that the composition according to thepresent invention has enhanced lubricity when compared with fuelcompositions which have a low sulphur content but in which the fusedpolycyclic aromatic compound containing exocyclic nitrogen group isabsent. The amount of the fused polycyclic aromatic compound added tothe fuel composition is it least 50 ppm, suitably 70 ppm or more and ispreferably from 50-10,000 ppm by weight of the total fuel composition.In this context it will be understood by those skilled in the art thatthe improvement in antiwear and lubricity characteristics of the fuelcomposition may not bear a linear relationship commensurate with theamount of the fused polycyclic aromatic compound that is added to saidcomposition. Thus, addition of a vast excess of such an additive may notnecessarily continually improve the antiwear or lubricity properties ofthe fuel composition.

The fuel composition according to the invention may contain one or moreconventional fuel additives, which may be added at the refinery, at thefuel distribution terminal, into the tanker, or as bottle additivespurchased by the end user for addition into the fuel tank of anindividual vehicle. For diesel fuels these additives may include coldflow improvers (also known as middle distillate flow improvers), waxantisettling additives, diesel fuel stabilizers, antioxidants, cetaneimprovers, combustion improvers, detergents, demulsifiers, dehazers,lubricity additives, anti-foamants, anti-static additive, conductivityimprovers, corrosion inhibitors, drag reducing agents, reodorants, dyesand markers, and the like.

The antiwear and lubricity performance of the fuel compositions of thepresent invention were measured according to the so-called highfrequency reciprocating rig test (hereafter referred to as “HFRR”). TheHFRR test consists of a loaded upper ball 6 mm in diameter, whichoscillates against a static lower plate. Both friction and contactresistance are monitored throughout the test. The tests are conductedaccording to the standard procedure published as CEC F-06-A-96 in whicha load of 2N (200 g) was applied, the stroke length was 1 mm, thereciprocating frequency was 50 Hz and sample temperature was 60° C. Theambient temperature and humidity were controlled within the specifiedlimits and the calculated value of wear scar diameter was corrected tothe standardized water vapour pressure of 1.4 kPa. The specimen ball wasa grade 28 (ANSIB3.12), AISI E-52100 steel with a Rockwell harness “C”scale (HRC) number of 58-66 (ISO 6508), and a surface finish of lessthan 0.05 μm R_(a), and the lower plate was AISI E-52000 steel machinedfrom anealed rod, with a Vickers hardness “HV30” scale number of 190-210(ISO 6507/1). It is turned. lapped and polished to a surface finish of0.02 μm R_(a).

Summary of HFRR test conditions Fluid volume, ml 2.0 ± 0.20 Specimensteel AISI E-52100 Fluid temperature, 60 ± 2  Ball diameter, 6.00 ° C.mm Bath surface area, 6.0 ± 1.0  Surface finish <0.05 μm Ra cm² (ball)Stroke length, mm 1.0 ± 0.02 Hardness (ball) 58-66 Rockwell C Frequency,Hz 50 ± 1  Surface finish <0.02 μm Ra (plate) Applied load, g 200 ± 1  Hardness 190-210 HV 30 (plate) Test duration, 75 ± 0.1  Ambient See textminutes conditions

The present invention is further illustrated with reference to thefollowing examples. The ULSADOs (50 ppm sulphur) used in this study aredescribed below in Table 1:

TABLE 1 Analysis ULSADO Density @ 15° C. 834.0 Viscosity KV₄₀ 2.52Sulphur content (ppm) 27 Nitrogen content (ppm) 27 Aromatics (% m/m)1-ring 20.55 2-ring 7.77 3-ring 0.68 Distillation IBPt 157 T5% 181 T10%196 T20% 222 T30% 246 T40% 264 T50% 276 T60% 286 T70% 293 T80% 301 T90%310 T95% 318 FBPt 331

The following compounds shown in Table 2 below were tested at thespecified concentrations:

TABLE 2 No. Name Conc (ppm wt/wt) 1 1-Aminonaphthalene 5,000 and 500 21,8-Diaminonaphthalene   500 and 250 3 Quinoline 5,000

TABLE 3 Conc Average Average wear No. Sample (ppm wt/wt) Friction scar(mm)  1* Base fuel A N/A 0.457 573 2 1-Aminonaphthalene 5,000   0.262275 3 1-Aminonaphthalene 500 0.398 544 4 1,8-Diaminonaphthalene 5000.271 306 5 1,8-Diaminonaphthalene 250 0.277 309  6* Quinoline 5,000  0.341 499 *represents a Comparative Test (not according to theinvention)

The results presented show that the addition of compounds with anexocyclic nitrogen group improve the lubricity (wear and friction)relative to the base fuel when used alone. Comparison of quinoline and1-aminonaphthalene shows the improved performance for exocyclic nitrogencompounds versus their heterocyclic analogues. Furthermore it can beseen that the addition of a second exocyclic nitrogen group, in the formof 1,8 diaminonaphthalene, improves the performance further with goodactivity being maintained down to a treat rate of 250 ppm.

What is claimed is:
 1. A fuel composition having a sulphur content ofnot more than 50 ppm by weight and comprising a major amount of the fueland a lubricity enhancing additive of at least 50 ppm based on the totalweight of the fuel composition of at least one fused polycyclic aromaticcompound which comprises at least one exocyclic group containingnitrogen wherein the nitrogen is attached directly to a ring carbonatom, and wherein at least one aromatic ring in the aromatic compound isa heteroclic ring, wherein the heteroatom is nitrogen or oxygen.
 2. Afuel composition according to claim 1 wherein the sulphur content of thefuel composition is less than 40 ppm by weight.
 3. A fuel compositionaccording to any one of the preceding claims wherein the fuel is adiesel fuel.
 4. A fuel composition according to claim 1 wherein theexocyclic group containing nitrogen is a primary or a secondary aminogroup.
 5. A fuel composition according to claim 1 wherein said compoundcomprises more than one exocyclic nitrogen group and wherein saidnitrogen groups are positioned on adjacent carbon atoms.
 6. A fuelcomposition according to claim 1 wherein the fused polycyclic aromaticcompound which comprises at least one exocyclic group containingnitrogen is 2-(2-aminophenyl)indole.
 7. A fuel composition according toclaim 1 wherein the amount of the fused polycyclic aromatic compoundwhich comprises at least one exocyclic group containing nitrogen isadded to the fuel composition in an amount of 50-10,000 ppm by weight ofthe total fuel composition.
 8. A fuel composition according to claim 1wherein the fused polycyclic aromatic compound which comprises at leastone exocyclic group containing nitrogen and wherein the nitrogen isattached directly to a ring carbon atom of the polycyclic aromaticcompound is capable of acting as an antiwear and/or lubricity enhancingadditive for a low sulphur fuel.
 9. A fuel composition according toclaim 5 wherein the nitrogen atom in the exocyclic nitrogen compriseshydrogen and/or hydrocarbyl groups, preferably selected from aliphatic,cycloaliphiatic and aromatic hydrocarbyl groups.